Sometimes these are obvious (for example, increases in alanine aminotransferase (ALT), indicating liver injury) [40], and sometimes they are more subtle (for example, recently described changes in plasma Abeta 1–40 and 1–42 and phospho-tau indicating the onset of Alzheimer’s disease) [41,42,43], but either way these protein changes can be helpful for disease diagnosis. Here, GPT is linked to early-onset autosomal dominant Alzheimer disease.